Water heaters piped in parallel

I have 2 50gallon hot water heaters piped in parallel for a 6unit apartment building. A few days before Christmas I replaced one of them because it was leaking, but not the other. (mistake number 1). The new hot water heater is now several inches higher than the older one.

Doing some "pipe-grabbing" while a hot faucet is on, it looks like the new one is being used a little more than the old one although both are running. I tried closing the ball valve on the output of the new one just a little to create some restriction so I can balance the two water heaters out. Any drawbacks to this??

Greek Guy7, do some research before you replace your heater. Every heater manufacturer that I know of advises that the best set-up is a parallel installation.

We have always installed heaters in parallel and have never had a problem. We have also changed installs from series TO parallel and it always cures the problems. Also when installing more than 2 heaters they are done in parrallel.

Series is not as efficient and does not allow shutting off one heater at a time if there is an outage or a leaker. With series you might as well have only one heater because when one goes out they both have to be shut down.

The important thing is to remember to balance the piping so that the resistance is the same for each heater and the draw is equalized.

Dubldare's pdf link implies that both parallel water heaters are set to equal temperatures - which causes the first WH to wear faster. I think most WHs in Series are configured to step the temperature, the first raising the temp to ~75F and the second to final temp ~ 140F.

I think most WHs in Series are configured to step the temperature, the first raising the temp to ~75F and the second to final temp ~ 140F.

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1) I'm new to this forum, but not to plumbing and I hate to disagree, but,I suggest that you check the water heater manufacturers' websites and see if any advise the use of a series installation. If so please post a link.

2) Setting a water heater to only 75 degrees ( if the thermostat will even go that low) will set up a heck of a condensation problem and rot out a heater way before its time.

3) It is not an exact science, but you can match the piping lengths on the original install and in the future use a water heater that comes as close as possible to the old heater.

4) Especially in multi-family dwellings the parallel installation gives you the ability to have one heater out of service and still use the other until the bad one is replaced. Try that with a series install.

5)If dielectric unions are plugging up, don't use them. Use a brass union and a brass nipple to keep the water way clear. Even though dielectric unions are approved they cause more trouble than they prevent.

6)Explain to me how you successfully hook up 3 water heaters in series and provide fpr individual shut offs. Easy to do in parallel.

you absolutley KNOW that it will give you 100 gallons of water no matter which heater begins to clog up first....

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In total agreement on that! I'm just a rookie but I can speak from first hand knowledge on this issue.
When I had my old oil fired boiler it had the coil for hot water, never quite did the trick to my satisfaction. So I bought an electric 40 gallon and had the boiler feed it with pre-heated water and the electric took it the rest of the way. (In series)
I NEVER ran out of hot water, it was great. Then we coverted to gas and i lost my hook up <sigh>
I miss the old days LOL